In vitro screening of crude extracts from plants against Fusarium sacchari and Curvularia lunata and testing the efficacy of a selected crude extract of Alpinia galanga against grain discoloration and other rice diseases in the fields

Fifteen plant materials were extracted by 60% ethanol using maceration technique and tested against Curvularia lunata and Fusarium sacchari using poisoning food technique. The results indicated that dried Alpinia galanga rhizome extract at 10% concentration completely inhibited the mycelial growth of F. sacchari; while, 20% concentration of A. galanga extract highly inhibited the mycelial growth of C. lunata (78.3%). Therefore, the most effective one, dried A. galanga extract was selected and investigated in the field condition to suppress narrow brown leaf spot disease, neck blast disease, and grain discoloration (GD) disease in two growing seasons. After spraying two times, the results showed that 20% A. galanga ethanolic extract significantly reduced the incidence of narrow brown leaf spot disease (0.7) and (1.2) in both seasons and suppressed the severity of neck blast disease (12.5%) in the second season. For GD disease severity, 20% concentration of galangal extract showed the lowest disease severity (3.5) among all treatments. The galangal extract was effective to suppress the other important rice diseases, narrow brown leaf spot, and neck blast diseases under field conditions.